{"id":199724,"date":"2025-05-06T09:55:59","date_gmt":"2025-05-06T01:55:59","guid":{"rendered":"https:\/\/server.hk\/cnblog\/199724\/"},"modified":"2025-05-06T09:55:59","modified_gmt":"2025-05-06T01:55:59","slug":"%e7%a0%94%e7%a9%b6-mysql-%e4%b8%ad%e7%9a%84-isnull-%e5%87%bd%e6%95%b0%e5%8f%8a%e5%85%b6%e5%ba%94%e7%94%a8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/199724\/","title":{"rendered":"\u7814\u7a76 MySQL \u4e2d\u7684 ISNULL \u51fd\u6570\u53ca\u5176\u5e94\u7528"},"content":{"rendered":"

<\/b> <\/p>\n

\u7814\u7a76 MySQL \u4e2d\u7684 ISNULL \u51fd\u6570\u53ca\u5176\u5e94\u7528<\/h1>\n

\u6b22\u8fce\u5404\u4f4d\u5c0f\u4f19\u4f34\u6765\u5230\u4e3b\u673a\u5b9d\u8d1d\uff0c\u76f8\u805a\u4e8e\u6b64\u90fd\u662f\u7f18\u54c8\u54c8\u54c8\uff01\u4eca\u5929\u6211\u7ed9\u5927\u5bb6\u5e26\u6765\uff0c\u8fd9\u7bc7\u6587\u7ae0\u4e3b\u8981\u8bb2\u5230\u7b49\u7b49\u77e5\u8bc6\uff0c\u5982\u679c\u4f60\u5bf9\u76f8\u5173\u7684\u77e5\u8bc6\u975e\u5e38\u611f\u5174\u8da3\u6216\u8005\u6b63\u5728\u81ea\u5b66\uff0c\u90fd\u53ef\u4ee5\u5173\u6ce8\u6211\uff0c\u6211\u4f1a\u6301\u7eed\u66f4\u65b0\u76f8\u5173\u6587\u7ae0\uff01\u5f53\u7136\uff0c\u6709\u4ec0\u4e48\u5efa\u8bae\u4e5f\u6b22\u8fce\u5728\u8bc4\u8bba\u7559\u8a00\u63d0\u51fa\uff01\u4e00\u8d77\u5b66\u4e60\uff01<\/p>\n

\u6807\u9898\uff1a\u6df1\u5165\u63a2\u7a76MySQL\u4e2dISNULL\u51fd\u6570\u7684\u529f\u80fd\u53ca\u7528\u6cd5<\/p>\n

MySQL\u662f\u4e00\u79cd\u6d41\u884c\u7684\u5173\u7cfb\u578b\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\uff0c\u800c\u5728\u5176\u51fd\u6570\u5e93\u4e2d\uff0cISNULL\u51fd\u6570\u662f\u5e38\u7528\u7684\u51fd\u6570\u4e4b\u4e00\u3002\u672c\u6587\u5c06\u63a2\u7a76ISNULL\u51fd\u6570\u7684\u529f\u80fd\u548c\u7528\u6cd5\uff0c\u5e76\u63d0\u4f9b\u8be6\u7ec6\u7684\u4ee3\u7801\u793a\u4f8b\u3002<\/p>\n

1. ISNULL\u51fd\u6570\u7684\u529f\u80fd\u4ecb\u7ecd<\/h3>\n

ISNULL\u51fd\u6570\u5728MySQL\u4e2d\u7684\u4f5c\u7528\u662f\u5224\u65ad\u8868\u8fbe\u5f0f\u662f\u5426\u4e3aNULL\uff0c\u5e76\u5728\u6761\u4ef6\u4e3a\u771f\u65f6\u8fd4\u56de1\uff0c\u6761\u4ef6\u4e3a\u5047\u65f6\u8fd4\u56de0\u3002\u8fd9\u4e2a\u51fd\u6570\u5728\u5904\u7406\u6570\u636e\u5e93\u4e2d\u7684\u7a7a\u503c\u65f6\u975e\u5e38\u6709\u7528\uff0c\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u8fdb\u884c\u6709\u6548\u7684\u6570\u636e\u5904\u7406\u548c\u5224\u65ad\u3002<\/p>\n

2. ISNULL\u51fd\u6570\u7684\u7528\u6cd5\u793a\u4f8b<\/h3>\n

\u4e0b\u9762\u901a\u8fc7\u51e0\u4e2a\u793a\u4f8b\u6765\u5c55\u793aISNULL\u51fd\u6570\u7684\u7528\u6cd5\uff1a<\/p>\n

\u793a\u4f8b\u4e00\uff1a\u5224\u65ad\u67d0\u5b57\u6bb5\u662f\u5426\u4e3a\u7a7a\u503c<\/h4>\n

\u5047\u8bbe\u6211\u4eec\u6709\u4e00\u4e2a\u5b66\u751f\u8868\uff08students\uff09\uff0c\u5176\u4e2d\u5305\u542b\u5b66\u751f\u7684\u59d3\u540d\u548c\u5e74\u9f84\u5b57\u6bb5\uff0c\u6709\u65f6\u5019\u5e74\u9f84\u5b57\u6bb5\u53ef\u80fd\u4e3a\u7a7a\u3002\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528ISNULL\u51fd\u6570\u6765\u5224\u65ad\u5e74\u9f84\u662f\u5426\u4e3a\u7a7a\u503c\u3002<\/p>\n

SELECT name, ISNULL(age) AS is_age_null\nFROM students;<\/pre>\n
\u4ee5\u4e0a\u67e5\u8be2\u5c06\u8fd4\u56de\u6240\u6709\u5b66\u751f\u7684\u59d3\u540d\u4ee5\u53ca\u4e00\u4e2a\u5e03\u5c14\u503c\uff0c\u8868\u793a\u8be5\u5b66\u751f\u7684\u5e74\u9f84\u5b57\u6bb5\u662f\u5426\u4e3a\u7a7a\u3002<\/p>\n
\u793a\u4f8b\u4e8c\uff1a\u5c06NULL\u503c\u66ff\u6362\u4e3a\u6307\u5b9a\u503c<\/h4>\n
\u6709\u65f6\u5019\u6211\u4eec\u5e0c\u671b\u5c06NULL\u503c\u66ff\u6362\u4e3a\u7279\u5b9a\u7684\u503c\uff0c\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u53ef\u4ee5\u7ed3\u5408ISNULL\u548cIF\u51fd\u6570\u6765\u5b9e\u73b0\uff1a<\/p>\n
SELECT name, IF(ISNULL(age), '\u672a\u77e5', age) AS age\nFROM students;<\/pre>\n
\u4ee5\u4e0a\u67e5\u8be2\u5c06\u8fd4\u56de\u6240\u6709\u5b66\u751f\u7684\u59d3\u540d\u4ee5\u53ca\u5e74\u9f84\u5b57\u6bb5\uff0c\u5982\u679c\u5e74\u9f84\u5b57\u6bb5\u4e3a\u7a7a\uff0c\u5219\u5c06\u5176\u66ff\u6362\u4e3a”\u672a\u77e5”\u3002<\/p>\n
\u793a\u4f8b\u4e09\uff1a\u4f7f\u7528ISNULL\u8fdb\u884c\u6761\u4ef6\u5224\u65ad<\/h4>\n
ISNULL\u51fd\u6570\u8fd8\u53ef\u4ee5\u7528\u4e8e\u6761\u4ef6\u5224\u65ad\uff0c\u6bd4\u5982\u7b5b\u9009\u51fa\u5e74\u9f84\u4e0d\u4e3a\u7a7a\u7684\u5b66\u751f\uff1a<\/p>\n
SELECT name, age\nFROM students\nWHERE NOT ISNULL(age);<\/pre>\n
\u4ee5\u4e0a\u67e5\u8be2\u5c06\u8fd4\u56de\u6240\u6709\u5e74\u9f84\u5b57\u6bb5\u4e0d\u4e3a\u7a7a\u7684\u5b66\u751f\u3002<\/p>\n
3. \u603b\u7ed3<\/h3>\n
\u901a\u8fc7\u672c\u6587\u7684\u4ecb\u7ecd\uff0c\u6211\u4eec\u6df1\u5165\u63a2\u7a76\u4e86MySQL\u4e2dISNULL\u51fd\u6570\u7684\u529f\u80fd\u53ca\u7528\u6cd5\uff0c\u5e76\u63d0\u4f9b\u4e86\u8be6\u7ec6\u7684\u4ee3\u7801\u793a\u4f8b\u3002ISNULL\u51fd\u6570\u5728\u5904\u7406\u7a7a\u503c\u65f6\u975e\u5e38\u5b9e\u7528\uff0c\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u8f7b\u677e\u5904\u7406\u6570\u636e\u548c\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\u3002\u5728\u65e5\u5e38\u7684\u6570\u636e\u5e93\u7ba1\u7406\u548c\u67e5\u8be2\u4e2d\uff0c\u5408\u7406\u4f7f\u7528ISNULL\u51fd\u6570\u53ef\u4ee5\u63d0\u9ad8\u5de5\u4f5c\u6548\u7387\uff0c\u66f4\u597d\u5730\u64cd\u4f5c\u6570\u636e\u5e93\u4e2d\u7684\u6570\u636e\u3002<\/p>\n
\u4eca\u5929\u5e26\u5927\u5bb6\u4e86\u89e3\u4e86\u7684\u76f8\u5173\u77e5\u8bc6\uff0c\u5e0c\u671b\u5bf9\u4f60\u6709\u6240\u5e2e\u52a9\uff1b\u5173\u4e8e\u6570\u636e\u5e93\u7684\u6280\u672f\u77e5\u8bc6\u6211\u4eec\u4f1a\u4e00\u70b9\u70b9\u6df1\u5165\u4ecb\u7ecd\uff0c\u6b22\u8fce\u5927\u5bb6\u5173\u6ce8\u4e3b\u673a\u5b9d\u8d1d\u516c\u4f17\u53f7\uff0c\u4e00\u8d77\u5b66\u4e60\u7f16\u7a0b~<\/p>\n
\n
\n <\/dt>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"
\u7814\u7a76 MySQL \u4e2d\u7684 ISNU...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-199724","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/199724","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=199724"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/199724\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=199724"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=199724"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=199724"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}